The disclosure of Japanese Patent Application No. 11-313614 filed on Nov. 4, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a method of producing an interior trim material. More particularly, the present invention relates to a method of producing an interior trim material, such as a ceiling materials or a door trim for use in automobiles, in which a skin material is bonded to a substrate,.
2. Discussion of Related Art
Conventionally, an interior trim material comprised of a rigid substrate and a skin material bonded to at least one surface thereof has been widely used in the interior or vehicle compartment of an automobile.
In this case, inorganic fibers and thermoplastic fibers are mainly used for producing the substrate. The inorganic fibers provide certain rigidity and dimensional stability, and the thermoplastic fibers provide certain formability, while the skin material provides a certain design quality.
A known example of method (hereinafter referred to as xe2x80x9cknown method 1xe2x80x9d) of producing an interior trim material having the above-described substrate and the skin material bonded to the surface thereof includes three processes, i.e., a process of producing a substrate, a process of tentatively bonding a skin material to the substrate, and a forming process.
In the substrate production process of the known method 1, the substrate is prepared by laminating a thermoplastic resin film or films onto either one or both of the opposite surfaces of a mat-like fiber structure mainly formed from inorganic fibers containing thermoplastic fibers. This substrate is then fed onto an endless belt formed from a Teflon sheet that is bonded to the substrate when the thermoplastic resin film is in a molten state but not bonded thereto when the same film is not in a molten state, and is then heated in a furnace.
Subsequently, the substrate thus heated is compressed under pressure by a pressing portion on the endless belt so that the mat-like fiber structure is impregnated with the thermoplastic resin film. At the same time, the inorganic fibers contained in the mat-like fiber structure are firmly bonded together by means of the thermoplastic fibers contained in the mat-like fiber structure. The substrate thus compressed under pressure is thereafter naturally or forcibly expanded so as to restore its original thickness, and the cooled at a cooling portion on the endless belt. In this manner, a substrate is produced in which inorganic fibers are bonded together by thermoplastic resin and thermoplastic fibers.
In the next process of bonding the skin material, the substrate produced in the above step is cut into a suitable size, and a skin material is laminated on the cut piece of the substrate, and locally melted by heat so as to be tentatively bonded to the substrate.
Finally, in the forming process, the substrate to which the skin material has been tentatively bonded is reheated in the furnace so that the thermoplastic fibers and thermoplastic resin are melted. A cold press machine is then used to form the substrate with the skin material into a desired shape, thereby to provide an interior trim material consisting of the substrate and the skin material bonded to the substrate.
Japanese Patent Laid-Open Publication No. HEI 8-80601 discloses a method in which a skin material as well as a substrate is fed onto an endless belt in the substrate production process as described above, thereby eliminating the process of tentatively bonding the skin material to the substrate, and a flat composite sheet with the skin material can be produced in a single process step.
According to a method of producing an interior trim material as disclosed in Japanese Patent Laid-Open Publication No. 10-315396 (hereinafter referred to as the xe2x80x9cknown method 2xe2x80x9d), a mat-like fiber structure formed from thermoplastic fibers and glass fibers is prepared, and hot air having a temperature high enough to melt the thermoplastic fibers is caused to pass through the fiber structure from the front side to the back side thereof, thereby providing a substrate in which the density distribution of the thermoplastic resin has been thus varied. Then, a skin material with thermoplastic resin formed on its back surface, which has been heated such that the thermoplastic resin is given certain plasticity, is laminated on a surface of the substrate provided in the above manner. The thus laminated skin material and substrate are then formed into a desired shape by press molding using a forming die, so as to form a substrate in which the glass fibers are bonded together by thermoplastic fibers, while at the same time bonding the skin material to the substrate, thereby to produce an interior trim material.
In the known method 1 as described above, the substrate is heated in the furnace so that the thermoplastic fibers and thermoplastic resin are melted, and the substrate thus heated is compressed under pressure so that the inorganic fibers are firmly bonded together by the thermoplastic fibers and thermoplastic resin, whereby the resulting substrate is given rigidity.
In the known method 1, a series of steps included in the substrate production process are carried out by use of the endless belt. This eliminates such a problem that melted thermoplastic resin sticks to local parts of a press mold or die, or the like, when the substrate is compressed under pressure, resulting in a failure to transport the substrate to the following process step. Thus, the substrate can be favorably produced with high reliability and efficiency.
The endless belt used in the known method 1, however, is required to have sufficiently high heat resistance, durability, and rigidity, and therefore cannot be suitably used for forming interior trim materials having complicated shapes. Thus, in the process step of impregnating the mat-like fiber structure with the thermoplastic resin film, the heated substrate material is compressed under pressure, only to be formed into the shape of a flat plate or sheet. Namely, the substrate can be formed only in the shape of a flat plate or sheet.
In order to form a substrate into a desired shape other than the flat shape, therefore, it is necessary to re-heat the substrate to soften the thermoplastic fibers and thermoplastic resin, so as to form the substrate into the desired shape in another process without using an endless belt, for example, in the forming process of the known method 1. If the substrate, in which organic fibers have been firmly bonded together by thermoplastic resin and thermoplastic fibers through the process of impregnating the substrate with the thermoplastic resin, is reheated, however, the bonding strength of the fibers in the substrate is weakened, and the strength of the resulting substrate is reduced. If the density (mass per unit area) of the substrate is increased so as to ensure a required strength of the substrate, the weight of the substrate may be undesirably increased, and the production cost may also be undesirably increased.
In the known method 2 as described above, on the other hand, only one heating step is required in the whole manufacturing process beginning with the production of the substrate and ending with the production of the interior trim material to which the skin material is bonded.
In the method as described above, the substrate through which hot air has been passed and the skin material backed with the melted thermoplastic resin and laminated on the substrate are formed directly into a desired shape using a suitable die. In order to provide sufficiently high bonding strength with the skin material by impregnating the substrate with the backing resin, the die clearance of the forming die needs to be reduced. This may result in a reduction in the substrate thickness, and insufficient rigidity due to the reduced substrate thickness. If the die clearance of the forming dies is increased, on the contrary, the compressing force may be reduced, resulting in insufficient bonding of inorganic fibers by use of the thermoplastic fibers contained in the substrate. It is thus difficult or impossible to provide sufficiently high rigidity of the substrate through the bonding of the inorganic fibers, and provide sufficiently high bonding strength with the skin material.
It is therefore an object of the present invention to provide a method of producing an interior trim material, which makes it possible to easily produce an interior trim material including a substrate with sufficient rigidity and a skin material bonded to the substrate, by carrying out simple process steps.
The inventors of the invention have found, as a result of studies, that the substrate and the skin material may be compressed under pressure by means of a flat type hot press machine while the thermoplastic resin is being melted, so as to assure sufficiently high bonding strength of the skin material bonded to the substrate while assuring sufficiently high rigidity of the substrate.
The inventors have also found that in order to produce an interior trim material having a desired shape while assuring sufficient rigidity of the substrate, the substrate and the skin material that have been compressed under pressure by the flat type hot press machine may be expanded to restore its original thickness, and then formed into the desired shape by a cold press machine while the thermoplastic resin is being softened.
The inventors have also found that in order to prevent thermoplastic fibers contained in the substrate from sticking or adhering to the flat type hot press machine while the substrate and skin material are compressed under pressure by means of the hot press machine, the substrate may be constructed such that a high-melting-point fiber sheet composed of high-melting-point fibers is to be located in contact with the hot press machine.
On the basis of the above findings, the inventors have developed the present invention, which provides a method of producing an interior trim material, comprising the steps of: forming a laminated structure by laminating a skin material, a mat-like fiber structure, and a high-melting-point fiber sheet on each other to be arranged in this order, the mat-like fiber structure being prepared by blending thermoplastic fibers and inorganic fibers, the high-melting-point fiber sheet comprising high-melting-point fibers having a melting point higher than that of the thermoplastic fibers of the mat-like fiber structure, at least the mat-like fiber structure being heated such that the thermoplastic fibers are melted; compressing the laminated structure under pressure by a hot press machine; expanding the laminated structure that has been compressed, so as to restore at least part of the thickness thereof; and forming the laminated structure into a certain shape by a cold press machine, while the thermoplastic fibers of the mat-like fiber structure maintains plasticity.
In short, the present invention is concerned with a method of producing an interior trim material having a substrate and a skin material bonded integrally to the substrate, wherein the substrate comprises a mat-like fiber structure prepared by blending thermoplastic fibers with inorganic fibers, and a high-melting-point fiber sheet.
In the method of producing an interior trim material according to the present invention, the substrate includes two layers, i.e., the mat-like fiber structure and the high-melting-point fiber sheet, the latter being one constituent element of the substrate. In addition, the skin material is laminated on the side of the mat-like fiber structure of the substrate, and thus bonded to the substrate. With the high-melting-point fiber sheet provided as one constituent element of the substrate, the interior trim material can be more easily and simply produced as compared with conventional ones. Namely, when the substrate and the skin material are compressed under pressure by the hot press machine, melted thermoplastic fibers can be prevented from sticking to dies of the hot press machine since the mat-like fiber structure containing thermoplastic fibers is laminated between the skin material and the high-melting-point fiber sheet.
The method of producing an interior trim material according to the present invention includes a laminated structure forming process, a compressing process, a thickness restoring process, and a forming process, but does not include a cooling process in the middle of producing the interior trim material. Thus, the interior trim material can be produced without setting or solidifying the melted thermoplastic fibers, thus eliminating a need to melt the thermoplastic fibers again. This prevents a reduction in the rigidity of the substrate which would otherwise occur due to repeated melting of the thermoplastic fibers. Also, the cooling process is not required, and therefore the time required for producing the interior trim material can be shortened.
Furthermore, according to the method of the present invention, the thermoplastic fibers contained in the mat-like fiber structure may be substantially entirely and sufficiently melted, making it possible to firmly bind the inorganic fibers together, thus assuring improved rigidity of the substrate.
In addition, the method of producing an interior trim materials according to the invention may employ a flat-type hot press machine that provides a flat die surface or surfaces. This allows the laminated structure to be uniformly pressed and compressed. It is therefore possible to cause the melted thermoplastic fibers to bind the inorganic fibers together more uniformly throughout the substrate, thus assuring improved rigidity of the substrate. Also, the melted thermoplastic fibers may penetrate into the high-melting-point fiber sheet so as to bond the mat-like fiber structure integrally with the high-melting-point fiber sheet to form the substrate. In addition, the substrate and the skin material may be firmly bonded to each other over the entire area thereof.
According to the method of the present invention, the laminated structure that has been compressed is naturally or forcibly expanded so as to be given a sufficient thickness, thus assuring sufficient rigidity of the substrate.
In the method of the invention, the laminated structure is formed into an intended shape using a cold press machine in the forming process while the thermoplastic fibers keep plasticity, namely, while the thermoplastic fiber are softened. This may avoid a reduction in the rigidity of the substrate that would otherwise occur due to re-heating of the thermoplastic fibers. Furthermore, since the laminated structure is formed by the cold press machine after it has expanded to a certain thickness, a sufficiently large forming clearance can be provided in the cold press machine. With the thickness of the substrate thus increased, the rigidity of the interior trim material may be further improved.